Driveshaft yoke/ujoint/markings alignment and balance concern - PeachParts Mercedes-Benz Forum

brilliantblue · #1 09-18-2016, 01:34 AM

Hey all! THanks for reading.

I recently had my family's shop (about an hour away) do some work on my 1984 300D. It got a new carrier bearing, u-joint, and some front end work.

And now it has a rattle that is shaking through the driveshaft tunnel and in the rear! My brother reported that it had a vibration, but that one day he took it out with a mind to figure out what was going on, and the vibration just went away. Indeed, when I drove off with it there was little vibration if any until I got back to my city and had to start from a stop light. Then it shook like hell! That vibration came and went as I drove it around town for work while trying to figure out what to do next.

So I searched and learned more than I ever wanted to know about driveshafts, and then put the rear wheels on stands and started looking around under the car.

Here's the thing - everything appears indexed - front and rear flanges across the flex discs to differential/tranny flanges. However, the factory = on the u-joint knuckle is not aligned with the - just past the sleeve nut.

Now, I've also seen it said in these parts that the flanges/yokes need to be aligned front to rear - I assume that means that if the rear shaft flange is pointing down then the front shaft flange should also be pointing down. Is this correct? Or does it matter. The shaft flanges DO "point down" together, and appear to be aligned through the spline and not one notch off to either direction.

My theory is that perhaps the u-joint knuckles didn't go back the same way they were originally. Like if one was numbered 1 & 3, and the other was 2 & 4, then they got switched from 1/2/3/4 to 1/4/3/2. Make sense?

Except, when I rotate it all around and visualize how changing that would affect things, I can tell that then the flanges wouldn't line up. And, I recognize that what would have been flipped would be relatively small piece of the overall shaft - u-joint knuckle to the splines.

So, the factory marks are not aligned, but the majority of the shaft is aligned. The factory marks are maybe at 12 o'clock and 4 o'clock.

My brother was not aware of the factory marks. And this car was made in January 1984, so could it even be possible it was during the time that MB had cast them but wasn't using them?

Also they (in trying to cure rattle) replaced the transmission mount, and I replaced the differential mount after getting it back. I didn't drive it prior to the transmission mount replacement, but the differential mount replacement did soften the rattle. However, around this time, the rattle stabilized into consistent onset around 38 mph and being the worse slightly faster - maybe by 42 mph, then smoothing out quite a bit with speeding up, but not all the way disappearing.

Tonight I looked everything over again and replaced the flex-discs (adding my own new index marks). The old MB "transmission" flex disc had a crack that was visible when moving the driveshaft around. The rear one seamed fine if maybe a little "alligatoring" on the surface, as though it had been clear-coated and that had crackled. Driving after flex disc replacement revealed improved performance, but still vibration at the same speeds.

Both they and I have done the loosening, rolling, retightening procedure for sleeve nut, trans mount, and carrier bearing.

Please advise! Junk yard drive shaft is starting to sound appealing.

My brother suspected a half-axle issue. I replaced both of those earlier this year with CVJ rebuilds after a catastrophic failure. However, this vibration did not appear after THAT repair!

I did discover that the driverside rear wheel hub has a touch of play in it, which seems to have gotten worse since my initial drivetrain inspection. It once simply made a "tink" sound when I yanked on it, but now has a little bit of jiggle. Could this cause a vibration up through the driveshaft that would rattle the change in my center console?

Sorry if this is TMI - but I wanted you to know all from the onset! Thanks again for any help!

Stretch · #2 09-18-2016, 02:28 AM

From the information given with regards to the propshaft I plucked out this =>

Quote:

Originally Posted by brilliantblue

...Both they and I have done the loosening, rolling, retightening procedure for sleeve nut, trans mount, and carrier bearing.

Please advise! Junk yard drive shaft is starting to sound appealing.

...

Replacing the propshaft probably isn't going to help.

If you have gone through the procedure of having a slackly assembled system - roll the car back and forth - then tighten stuff back up with out lifting the car then you've done what you can...

...now it is time to consider the relative heights of the engine + transmission, the centre propshaft bearing and the subframe + differential mount.

All of these components need to be aligned - with a straight line running from the front of the crankshaft pulley all the way to the differential input shaft. So check the condition of the motor mounts, the gearbox mount, the subframe mounts and the differential mount.

Quote:

Originally Posted by brilliantblue

...
I did discover that the driverside rear wheel hub has a touch of play in it, which seems to have gotten worse since my initial drivetrain inspection. It once simply made a "tink" sound when I yanked on it, but now has a little bit of jiggle. Could this cause a vibration up through the driveshaft that would rattle the change in my center console?

Sorry if this is TMI - but I wanted you to know all from the onset! Thanks again for any help!

Any feelable axial play in a rear wheel bearing on a W123 is potentially dangerous - get this fixed as a priority

optimusprime · #3 09-18-2016, 06:48 AM

An old tip for shafts running out of balance. Is to fit two hose clips on to the shaft, both together side by side .Then try the car out, if no change ,then unscrew one and turn it a fraction at a time ,then lock it up.. Then it trial and error ,till you get it to run quiet .

brilliantblue · #4 09-18-2016, 01:38 PM

I just saw that idea last night!

i assume this would be in the larger part of the shaft, where it is essentially unobstructed.

i did notice it used to sometimes seem start vibrating right between the seats, then move back to the rear of the car as i sped up. I played around with using washers under the carrier bearing to see if that changed anything, but the vibration was so inconsistent at that time that i couldn't tell a difference. it definitely didn't go away!

i'm planning the wheel bearing and engine mounts next. But I will try this hose clamp suggestion.

Thanks for the help guys!

Diesel911 · #5 09-18-2016, 02:51 PM

See post #5 for pic.
1985 300cd driveshaft?

You also might want to re-examine the Flex Discs for cracks and so on.

If you do a www.images.google.com search for "Mercedes 300D U-joint alignment marks." it brings up some different sites on the subject.

SD Blue · #6 09-18-2016, 03:25 PM

Several things to check:
The factory marks definitely need to be aligned =-
Does the front shaft have a balance disc near the fix disc? If so, there are marks on it as well. (look for an arrow)
One of the most critical items is the mating of the flex discs and flanges and the relative hardware.
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Chassis/41-100.pdf
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/chassis_82_do.htm
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/chassis_82_do.htm
Once you have all of that sorted out, then the trick of leaving the carrier bearing support and prop shaft nut loose for the final back and forth adjustment.

These propeller shafts are very light weight and it takes very little to unbalance them. (Just look at the balance weight on the shaft itself.) I fought an unbalance problem on mine, for months, after a shop worked on mine. Only after complete disassembly and following the FSM to a "T", I managed to smooth things out.

brilliantblue · #7 09-18-2016, 05:43 PM

Thanks for the info SD BLUE - I appreciate the FSM links especially.

If I align the - = marks, my flanges will no longer be "synced". Is this an issue? Additionally, the shops original index marks will not align if I match these - = marks. (Currently the shop marks are matched up) As I previously mentioned, I believe the short spline to knuckle section got flipped during the u-joint installation. Regardless of that, however, it does not appear that the flanges would sync if that piece was flipped.

So, one question is: Is there anything to the idea that the flanges should be "synced" (pointing the same direction)? Or is that a bunch of fooey?

Also, no balance disc present

compu_85 · #8 09-18-2016, 05:48 PM

From what I have seen* the yolk alignment doesn't mean anything. The important thing is the = and - mark on the driveshaft tubes.

(*NOS 350SD driveshaft and reman 350SDL driveshaft)

-J

SD Blue · #9 09-18-2016, 05:59 PM

I haven't seen anything in the FSM, or elsewhere, that supports flanges in sync. The original shaft was never balanced that way from what I've seen. I think you'll have a whole lot less frustration if you follow the FSM. Personally, I haven't heard of anyone here having success with home remedies for obtaining a vibration free prop shaft.

Dan Stokes · #10 09-18-2016, 06:23 PM

It turns out that many smart phones have built-in accelerometers and there's an app that will display the vibration that the phone is detecting. You can place the phone on whatever is shaking the most and use it to detect the point at which the shaft comes more into balance.

A friend of mine has a 455 Buick big block in a Skylark and has been fighting driveline shake following having a new shaft made (he lives in a rural area so taking the shaft to a local shop is not an option). Anyhow, he's been messing with the 2 hose clamps system, using the phone to monitor his success and he's come up with a MUCH better balanced system. He's put the car up on jackstands and drives the car while sensing shaking on his center console. Be sure that the stands are holding up the suspension so that the driveline geometry is as close to "driving down the road" as possible. If you need more info I'm PM you with contact info.

Dan

leathermang · #11 09-18-2016, 09:04 PM

Quote:

Originally Posted by Stretch

.....

...now it is time to consider the relative heights of the engine + transmission, the centre propshaft bearing and the subframe + differential mount.

All of these components need to be aligned - with a straight line running from the front of the crankshaft pulley all the way to the differential input shaft. So check the condition of the motor mounts, the gearbox mount, the subframe mounts and the differential mount.....

ALSO , I think that if there are three units in a propeller shaft... that the angles are made by the u joints are supposed to be equal. Well, even if there are only two u joints and one main shaft the angles are supposed to be equal...
I do not understand the part about ' front of crankshaft pulley' ... that being the front of the engine.... the purpose of u joints is to correct that non alignment... which almost no cars have.

brilliantblue · #12 09-19-2016, 12:48 AM

Thanks for all the ideas! I'll try some things on Tuesday eve and report back!

Stretch · #13 09-19-2016, 07:29 AM

Quote:

Originally Posted by leathermang

ALSO , I think that if there are three units in a propeller shaft... that the angles are made by the u joints are supposed to be equal. Well, even if there are only two u joints and one main shaft the angles are supposed to be equal...
I do not understand the part about ' front of crankshaft pulley' ... that being the front of the engine.... the purpose of u joints is to correct that non alignment... which almost no cars have.

WELL - the point is that the majority of the W123, W126, W124 and W201 vehicles are fitted with a two piece propshaft. The idea that many people have that these vehicles are like some sort of Shelby race cart horse sprung arrangement is totally incorrect...

...the majority of these vehicles have ONE universal joint.

Crawl on your belly and look under your car to see for yourself.

In the situation where there is a bend in a two piece shaft that is connected by a single universal joint in the middle the bend will produce (inherent) vibration.

This inherent vibration is most commonly tackled by using a system of TWO universal joints - this system cancels out this inherent vibration (see wikepedia for yourself I can't be effing arsed to link to that information any more).

Mercedes have designed a system where the propshaft is kept straight. The effect of a "straight" UJ is that there is no / hardly any inherent vibration produced by the geometric simplicity of the universal joint.

The crucial thing to note with this Mercedes design is that when the car goes over uneven ground the rear wheels move up and down but the differential does not. The propshaft does NOT extend and contract.

(The up and down motion of the rear (driving) wheels is catered for by four constant velocity joints in the axles)

The whole point of the Mercedes design is that the output from the transmission (which just so happens to be the same "height" as the front of the crankshaft pulley) is at the same "height" as the input shaft (pinion) of the differential.

The resilient mounts on the engine + transmission + subframe (and differential) are important. If one or many of these mounts collapse then it is possible to have a kink in the SINGLE universal joint - you might / will get inherent induced vibrations in the driveline.

Pissing about with the clamping of jubilee clips isn't going to help if the drive line is not straight.

compu_85 · #14 09-19-2016, 10:18 AM

And to emphasize what Stretch said... the collar nut between the axle parts should be tight and the splines should not slip. That's part of why I had to replace my driveshaft... the nuts were loose and the splines got slop in them.

From the factory the ujoints should move very little, if at all.

If you have some time to kill you can see some of the troubles I went through on my car here: https://www.youtube.com/watch?v=7xqeine6rs8

-J

brilliantblue · #15 09-19-2016, 05:16 PM

I wondered if the collar wasn't tight enough when I was having intermittent trouble. I tried turning it but didn't have a proper wrench and didn't want to round off the nut with the channel locks i did have - i wasn't confident that i budged it. However, the vibration changed from intermittent to consistent afterward. This was during the session where I replaced the differential mount so I was considering THAT to be the difference.

So, perhaps the PO had some other trial with driveshaft issues and wound up having a mis-aligned driveshaft balanced. The - notch on mine is truly overlookable. Especially if you didn't know what to look for.

Maybe i need to do the roll again.